Katabolism and Heat Production. 497 



per cent of the total energy was derived from protein. The largest proportion 

 is on the third day of experiment No. 71, namely, 19.2 per cent. In the food 

 experiments the proportions derived from protein are not materially different 

 on the whole from those observed during fasting. 



An examination of the proportions of energy derived from fat shows con- 

 siderable variations, which are especially noticeable on the first days of the 

 longer fasting experiments. The apportionment of the carbon other than that 

 of protein between the fat and glycogen would lead to the supposition that as 

 the quantity of katabolized glycogen decreased, the amount of fat would be 

 increased, and this is actually what is found in comparing the amounts of 

 these two materials katabolized. Similar fluctuations in the energy derived 

 from the two compounds are also observed. No regularity appears in the 

 proportion of the energy resulting from fat. It is generally greater than 75 

 per cent, but in fasting experiments may be as small as 55 per cent. In one 

 instance, namely, on the last day of food experiment No. 76, it fell to 36.5 

 per cent. The highest proportion was found on the last day of experiment 

 No. 73. 



Since a much smaller proportion of the total energy results from glycogen 

 rather than from fat katabolism, the fluctuations in the proportions of the 

 energy supplied by the glycogen are very considerable, and it is difficult to ob- 

 tain any general average for the amount of energy furnished by this compound. 

 In two instances there was apparently an absorption of energy due to the 

 formation and storage of glycogen, 108 namely, on the last day of experiment 

 No. 73 and the second day of experiment No. 81. This apparent storage or 

 absorption of energy in the form of glycogen could only be derived from body 

 fat or protein, and hence the absorption of energy is apparent and not real. 

 The largest proportion of energy supplied by glycogen on any one day in the 

 fasting experiments was 37.8 per cent. On the last day of food experiment 

 No. 76, a maximum of 52.3 per cent was reached. 



COMPARISON OF PRODUCTS OF KATABOLISM AND HEAT PRODUCTION. 



It has commonly been assumed that heat production and katabolism are 

 interdependent and the older methods of computing the heat production were 

 based on this assumption. Therefore, experiments in which all the grosser 

 factors of katabolism have been studied present unusual opportunity for an 

 examination of the regularity of the course of the heat production compared 

 to that of the general katabolism. Such a comparison may be made in several 

 ways. The relations between the grosser factors, oxygen consumption, carbon 

 dioxide and water elimination, and heat production are first studied, and 

 later the numerous other products of katabolism, especially those appearing 

 in the urine, are compared. 



W8 For errors affecting the storage of glycogen see discussion of ratios of carbon 

 dioxide and oxygen to heat, p. 514. 

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